I'd like to use some old VSL gig instruments that are made for keyswitched legato, and meant to be used with the performance tool.Unfortunately, this tool only runs through wine, and then doesn't support jack midi, and can't be inserted as a plugin in ardour for example.

Ideally, I'd like a programmable midi filter lv2 plugin that I could set up to mimic VSL's performance tool. Is there such a thing? I tried learning about lv2 to create a specific plugin for this purpose, or modifying some existing plugin, but it's proven too complicated for me...

Any other options available that could be used (or modified) for this sort of thing?

The only midi-related lv2 plugins I know about are the pizmidi plugins (oringally VST, converted to lv2). Maybe you could use one of those as starting point.Also, you can use mididings which a python package to manipulate midi, though it runs standalone, not as an lv2 plugin.